The present invention relates to a process for producing a weather-resistant aromatic polycarbonate formed article with a coat having good surface properties such as high surface hardness. More particularly, the invention relates to a process for producing an aromatic polycarbonate formed article comprising forming a primer layer of a thermoplastic acrylic polymer on the surface of an aromatic polycarbonate formed article, then forming on said primer layer a protective topcoat comprised of cured organopolysiloxane.
Aromatic polycarbonates are transparent, lightweight, have good mechanical properties and are easily machinable. Because of these features, the aromatic polycarbonate is used in a structural member instead of glass, and for many other purposes. But as compared with metals and glass, the aromatic polycarbonate has low surface hardness, wear resistance, abrasion resistance and solvent resistance, and to expand its use, improving the surface properties of an aromatic polycarbonate formed article has been strongly needed.
Several attempts have been made to improve the surface properties of an aromatic polycarbonate formed article by coating a paint on the surface of the formed article to form a protective coat thereon. According to one method, a thermosettable melamine resin paint is applied to the polycarbonate formed article and heat-curing the same to form a protective coat. In another method, a polyfunctional acrylic compound is applied and cured by exposure to ultraviolet rays to form a protective coat. In still another method, a hydrolyzate of carbon-functional silane compound is applied and cured to form a protective coat comprised of organopolysiloxane. But the protective coat formed by each of these methods does not have a strong bond to the polycarbonate substrate, and it does not have satisfactory durability.
The cured organopolysiloxane layer provides good surface properties, but it does not have intimate contact with the polycarbonate substrate, and several methods have been proposed to provide improved intimate contact by treating the surface of the polycarbonate substrate before forming the protective coat. In one method, a paint containing a thermoplastic acrylic polymer is used as a surface treating agent [e.g. Japanese Patent Publication (Kohkai) No. 13856/77, and U.S. Pat. No. 4,224,378]. In another method, a paint containing a thermosettable acrylic polymer is used (e.g. U.S. Pat. No. 3,707,397). In still another method, a paint containing a bisphenol-type epoxy resin is used [Japanese Patent Publication (Kohkai) No. 40743/80].
As is well known, a layer made of cured organopolysiloxane is preferred as a coat having good surface properties, and many proposals have been made on the paint that provides a cured organopolysiloxane. But if a carbon functional silane compound is used as a paint, hostile curing conditions are necessary and a coating layer having optimum surface properties is hard to obtain, and one fatal defect is poor weather resistance. If a silicone functional silane compound is used, mild curing conditions can be used and the resulting coating layer has high weather resistance and better suits practical purposes. But the cured organopolysiloxane resulting from the silicone-functional silane compound usually has weak bonding power, so, to form a desired protective coat on the polycarbonate substrate, careful consideration is necessary with respect to the optimum combination of silicone-functional silane compound, surface treating agent and solvent.
The present invention provides a process for forming a coating layer with good surface properties on a polycarbonate formed article using a curable organopolysiloxane prepared by hydrolyzing a silicone functional silane compound. More particularly, the invention relates to a weather-resistant polycarbonate formed article having improved contact between the cured organopolysiloxane layer and polycarbonate substrate.
As described before, attempts have been made to use an acrylic polymer interlayer to increase the intimacy of contact between the cured organopolysiloxane layer and the polycarbonate substrate. The present inventors have made further studies on the use of a paint containing an acrylic polymer to form a primer layer on the polycarbonate substrate, and found that if a cured organopolysiloxane layer made of a silicone-functional silane compound is formed on a primer layer made of the commonly employed thermoplastic acrylic polymer, the resulting topcoat does not have the desired surface properties, especially high wear resistance.